Near-optimum trellis-coded DS/CDMA multiuser communications

We propose two classes of suboptimum receivers for coded direct-sequence code-division multiple-access (DS/CDMA) systems based on a generalized transmitter model. Compare to the optimum detector with complexity grows exponentially with the number of active user, the proposed detectors have linear complexity and near-optimum performance. The first class is to remove the multiple-access interference by modify the channel decoder. The second class is to separate the multiuser detection and channel decoder, and apply suboptimum multiuser detector at the front stage. Because the proposed detectors are based on a generalized model, the detectors can be applied for many different transmitter schemes. Numerical results show that the proposed detectors are able to alleviate the near-far problem and the performance achieved by those detectors is near that by the optimum detector.